Differential to single-ended converter circuits receive a differential signal composed of two input signals and convert the input signals to a single-ended output signal. Such circuits find application in the output stages of analog integrated circuits wherever a differential signal must be converted to a single-ended signal. For example, a differential amplifier that provides signals to an analog-to-digital converter would include a converter circuit as an output stage because analog-to-digital converters are typically designed to receive only single-ended signals.
Prior high speed converter circuits have a number of drawbacks. For one, they fail to maintain a linear relationship of output to input signal when the output signal voltage is measured relative to ground. For another, they tend to consume an undesirable amount of power to achieve linearity. Nonlinearity develops because of signal loss across PN junctions in the input stage and because of thermal distortion caused by the heating and cooling of such junctions during circuit operation. The undesirable power consumption arises from the increased standing current through the PN junctions required to improve linearity and from the increased gain needed in converting the signal. Typically, the output signal in conventional converters is measured with respect to ground and is proportional to only one of the input signals. In effect, half of the differential output signal is discarded. This loss in signal is compensated for by increasing the overall gain of the converter circuit, but at the cost of the increased power consumption. The additional power dissipated in turn causes more heating of the integrated circuit and increases the thermal distortion.